I agree that kids can be capable of many things—but 5 year olds? If the shooter had taken out all the closest teachers and then locked himself in a classroom with a bunch of 5 year olds, the odds are stacked in his favour even if he is outnumbered.
This was a kindergarten?
There might not be much, but I think when faced with do-or-die, even tykes would benefit from some advance planning as to what they might do. To swarm the attacker would incur some death, but would probably also bring the attacker down. But there would not be room for cowards.
Again, in such a society it goes without saying that adults too would face their duty with courage.